The last gas station in my home town has shut down the 98 pipes......So I need to adjust the ignition time a little, otherwise it's a very scratchy experience.

How many degrees do I need adjust - 4-5 degrees ? To little or to much......... has anyone tried this before.

RegardsHenrik

Have you actually tried it on 95?Do you know if your ignition is timed correctly?A tip I have heard about is to restrict the vacuum hose to the vacuum advance, thereby reducing the amount of vacuum advance when coasting and idling.

But more or less, I don't think it should be necessary. At least not from what I have heard about from other Matra owners e.g. at the meeting two weeks ago. I think most ran 95 anyway.

All Shell stations have 97 octane petrol btw, I use that when I can't find real 98.

Yep.. 98 is hard to come by these days... I run my car on shell v-power... since I live very close to a shell station.But on longer journeys it's a real concern how to obtain hi octane fuel.....I always keep a bottle or two of octane booster just in case..

Yes, the reason is that the octane booster from 95 to 98 is called MTBE - this MTBE is very poison and goes to the ground water......Less than 100 gas stations now has 98, and only because there is special protection.

I did try 95 (by mistake) some time ago - but I could hear the pre-ignition very heavy, and its not a nice sound

So adjustment is needed, but maybe I could try V-power with less adjustments.This is good idea, I will do so!

Hi Phil, and welcome to the forum! I hope you will enjoy it here Where are you from?Thank you for the very useful information, which leaves no doubt about what the factory claimed.Some of us are running modified engines, so we probably have to be a bit more careful...

The last gas station in my home town has shut down the 98 pipes......So I need to adjust the ignition time a little, otherwise it's a very scratchy experience.

How many degrees do I need adjust - 4-5 degrees ? To little or to much......... has anyone tried this before.

Hi Henrik,

It does seem to differ from car to car, which can be expected with any mass produced engine as they all tend to vary, but from my experience with four Murena 2.2 they all need higher octane than 95 RON to run correctly. I tried 95 RON some years ago and the engine pinked so badly it would not accelerate at even half throttle from around the torque peak (3000 rpm) which should be an easy point. Since most people cannot tell pinking (which is pre-ignition) from detonation, which can destroy an engine quite quickly, you do not want the 'death rattle' as I call it! The engines will run O.K. on 97 or 98 RON. Shell Powermax is 97 or 98 RON - do you not have that either?

You can retard the ignition to compensate but there is no set amount. You will have to find out by trial - start with 2 degrees and if you still get pinking, increase it a bit more, until you no longer have a problem. However, this will drop the power and I found that it was too much. An alternative if you can get it, is to add octane booster to the fuel. This is often found combined with the lead substitute additive. We are lucky so far here as we can get 97, 98 and even 100 octane from various pumps, or octane booster additive if anyone prefers to use that.

I have Anders, several times, and once after fitting something that was supposed to compensate for the lack of octane. The cars were undriveable! The fitting (Fuel Cat) was a total waste of time.

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A tip I have heard about is to restrict the vacuum hose to the vacuum advance, thereby reducing the amount of vacuum advance when coasting and idling.

That would be no use Anders. Think about it, you need to stop the low octane fuel pre-igniting or detonating under load. The light conditions when vacuum advance occurs - cruising or over-run (it has no effect when idling) are not the problem. So disconnecting the vacuum from, and stopping the distributor vacuum advance, will not stop the problem under load, i.e. accelerating, especially hard acceleration, at all.

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But more or less, I don't think it should be necessary.

Oh, I can assure you it is.

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At least not from what I have heard about from other Matra owners e.g. at the meeting two weeks ago. I think most ran 95 anyway.

Well I wouldn't trust that. Some time ago I heard owners saying they ran 95 octane with no problems which surprised me after my experiences; but when I went out with a couple of these people in their cars, I found the engines were pinking and the owners did not even realise it! So be careful.

As for Peugeot or Talbot information - I have seen different documents from them which contradict each other! They could never agree on whether you needed hardened valve seats or high octane fuel!! So I tend to ignore them.

I stand corrected... you are right of course about retarding being needed not during idle, but under load. Where did I keep my head?

I've never tried anything less than 97 octane myself, no need to try it then...

It is a bit worrying, however, what you are saying, Roy, considering Henriks' original subject of the thread - petrol stations where 98 are available are getting fewer in this country. I guess that means we need to tune the ignition if we want to run 95.

Henrik, I bought a little book some time ago which you might find useful in your tuning: SpeedPro Series, by Des Hammil: How to build & power tune distributor-type ignition systems. I got it from amazon.co.uk.